The field of the disclosure relates generally to centrifugal fans and, more specifically, to fan impellers with blades having an elliptical cross-section.
Fan impellers, such as centrifugal fan impellers, are used in a wide variety of applications. Many of these applications utilize a centrifugal impeller with a forward curved blade design, often referred to as a forward curved fan. A forward curved fan wheel has the advantage of being relatively compact in size for the amount of air that it can move. In contrast, a centrifugal fan wheel with backward curved blades is typically larger and must turn at a greater speed, than a comparable forward curved fan. It is for this reason that forward curved fans are used in many residential, commercial, industrial, and automotive applications.
However, a typical forward curved fan includes blade designs that provide stable and efficient airflow over a relatively narrow operating range. More specifically, at least some known forward curved fan impellers include blades whose cross-section is formed from a single radius, also known as a circular blade design. Furthermore, at least some known forward curved fan impellers include blades whose cross-sectional profile is formed by a combination of two or more unrelated radii such that an inner portion of the blade has a first radii and an outer portion of the blade has a second radii. A transition point is defined where the first radii shifts to the second radii.
Such blade profiles are known to cause separation of the airflow boundary layer from the blade at a point which decreases the efficiency of the impeller. More specifically, the boundary layer is defined between the blade's surface and a point above the surface of the blade where the air is undisturbed. Depending on the profile of the blade, the air will often flow smoothly in a thin boundary layer across the blade's surface. As air flows within the boundary layer, the momentum of the boundary layer flow slows over the length of the blade. A separation point is defined along the blade where the boundary layer separates from the blade and forms a turbulent flow. Boundary layer separation causes adverse pressure gradients in the wake behind the separation point, which decrease the efficiency of the blade. As such, it is advantageous for the boundary layer to remain attached to the blade along as long of a length as possible. However, known circular and combination blade profiles have constant rates of curvature that cause premature boundary layer separation and, therefore, decrease the blade's efficiency.